Multi-passage silencer for pneumatic tool



June 14, 1966 A. w. WALLACE MULTI-PASSAGE SILENGER FOR PNEUMATIC TOOL Filed Jan. 16, 1964 3 Sheets-Sheet 1 INVENTOR. ARTHUR W MIL/.405

A/EY June 14, 1966 A. w. WALLACE MULTI-PASSAGE SILENCER FOR PNEUMATIC TOOL 3 Sheets-Sheet 2 Filed Jan. 16, 1964 June 14, 1966 A. w. WALLACE 3,255,844

MULTI-PASSAGE SILENCER FOR PNEUMATIC TOOL Filed Jan. 16, 1964 3 Sheets-Sheet 3 +5 +|4 a9 +l3 5 a2 88 TTEJZ 7 15.13 FIE-I4 United States Patent 55,844 MULTI-PASSAGE SILENCER FOR PNEUMATIC TOOL Arthur W. Wallace, Denver, Colo., assignor to Gardner- Denver Company, a corporation of Delaware Filed Jan. 16, 1964, Ser. No. 338,037 21 Claims. (Cl. 181-36) This invention relates to mufiling devices, and more particularly to exhaust mufliing devices for pneumatic tools of the percussion type.

An object of this invention is to effectively suppress the sound Waves induced .by the emission of exhaust air from an air motor, such as a piston type air motor in a rock drill.

Another object of this invention is to provide one or more mufiiing devices, each for suppressing sound waves in a selected frequency range of the total sound spectrum induced by the exhaust air from a motor.

The novel features of the invention, as well as additional objects and advantages thereof, will be understood more fully from the following description when read in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a portion of a pneumatic tool casing including a motor chamber for a reciprocating piston hammer, and including muffiing devices communicating with the exhaust passage from the motor chamber.

FIG. 2 is a view of the assembly of FIG. 1, partially in section as viewed along the line 2-2 of FIG. 1 looking in the direction of the appended arrows.

FIG. 3 is a partial transverse sectional view, as viewed along the line 33 of FIG. 1.

FIG. 4 is a partial transverse section-a1 view, as viewed along the line 44 of FIG. 1.

FIG. 5 is a partial transverse sectional view, as viewed along the line 5-5 of FIG. 1.

FIG. 6 is a longitudinal sectional view of a portion of a pneumatic tool casing including a motor chamber for a reciprocating piston hammer, and including another arrangement of muflling devices communicating with the exhaust passage from the motor chamber.

FIG. 7 is a partialtransverse sectional view, as viewed along the line 7-7 of FIG. 6.

FIG. 8 is a fragmentary sectional view, as viewed along the line 88 of FIG. 7.

FIG. 9 is a partial transverse sectional view, as viewed along the line 9-9 of FIG. 6.

FIG. 10 is a partial transverse sectional view, as viewed along the line 10-10 of FIG. 6.

FIG.-l1 is a fragmentarysectional view, as viewed along the line 1111 of FIG. 6.

FIG. 12 is a longitudinal sectional view of a portion of a pneumatic tool casing having a motor chamber for a reciprocating piston hammer, and including still another arrangement of mufiling devices communicating with the exhaust passage from the motor chamber.

FIG. 13 is a partial transverse sectional view, as viewed along the line 13- 13 of FIG. 12.

FIG. 14 is a partial transverse sectional view, as viewed along the line 1414 of FIG. 12; and

FIG. 15 is a partial transverse sectional view, as viewed along the line 1'5-15 of FIG. 12.

In analyzing the noise created by a typical rock drill, it has been observed that noise of considerable intensity is created over substantially the entire audible frequency range. Some of the noise is mechanical noise created by the striking together and vibration of the mechanical parts i of the drill; and some of the noise is produced by sound pressure waves induced by. the air exhausted by the drill during its operation. At the very low end of the frequency range, noise is produced by the puffs of air which are exhausted from the hammer chamber at the end of the power stroke and return stroke of the piston hammer. The frequency of these puffs may be in the range of 60 to cycles per second; however, it has been observed that sound pressure waves induced at the harmonics of these frequencies are considerably more intense than the sound waves at the fundamental frequency. These harmonies contribute to produce a hump in the sound intensity curve in the range of 100 to 500 cycles per second, and the highest intensity noise produced by the rock drill occurs in this frequency range. Other noise created by the exhaust air may be termed jet noise; and this is noise produced by the rapid expansion of air passing from a relatively small passage or orifice to a relatively larger chamber or to atmosphere. It is believed that at least some of the jet noise is produced by shock waves resulting from the rapid expansion of air and, therefore, this noise may be reduced by reducing the rate of expansion of the air. It is believed that the jet noise is in frequencies generally above 1,000 cycles per second.

Referring to FIGS. 1 through 5 of the drawing, there is shown a portion of a rock drill of a well known type, such as a stoper drill. As best shown in FIG. 1, the rock drill includes a casing portion 1 and a back head portion 2, mounted at the rearward end of the casing. The internal bore of the casing 1 is larger at its rearward end and definesa chamber 3, adjacent to the back head, for

a valve block which would include a conventional distribution valve for controlling the reciprocation of the piston hammer. The forward end of the casing bore defines a cylinder chamber 4 for a piston hammer 5 having an enlarged head and a forwardly extending stem 6, the stem 6 extending slidably through a cylinder bushing and liner assembly 7 to strike a working implement. The casing 1 includes external longitudinally extending ribs 8 which enclose the usual air passages for controlling the operation of the drill.

An internal annular groove 9 is provided intermediate the ends of the cylinder chamber 4 and positioned to be exposed by the head of hammer 5 after each ofthe power and return strokes. A partial annular rib 10 is provided on the exterior of the casing and is disposed generally in the plane of the annular groove 9. Three pasages 11 extend through the rib 10 in a direction transverse to the plane of the groove 9; and these pasa-ges are communi-' cated with the annular groove by means of a milled slot -12 which is cut into the rib 10 from the groove, in the plane of the groove. It will be seen then that the annular groove 9, the milled slot 12 and the passages 11 define exhaust ports opening from the cylinder chamber 4 to exhaust the air from the chamber at the end of each of the power and return strokes of the hammer.

An elongated box-like housing 13 is mounted along one side of the casing enclosing the partial annular rib 10. The housing comprises parallel side walls 14, an outer wall 15 bridging the side walls 14, and an end wall 16 sealing the housing at the forward end thereof. Trvo transverse partitions 17 and 18 divide the housing into three separate and adjacent chambers. The partition 17 is joined to the rib and defines, with the end wall 16, a forward chamber 19 open to the forward ends of the passages 11. The partition 18 is spaced rearward of the partition 17 and defines with the partition 17 an intermediate chamber 20 open to the rearward ends of the passages 11. This partition also defines the rearward chamber 21 which is open to ambient atmosphere at its rearward end as will be described. Three holes 22 in the partition 1 8 communicate the chambers 20 and 21. The

side walls 14 and the outer wall 15 extend rearw-ardly be yond the casing 1 and overlies the back head 2. At the overlying position, the sidewalls 14 are provided with notches 24 which define lateral openings from the hous- .ing chamber 21 between the sidewalls and the back head. The rearward end of the chamber 21 is partially closed as will be described subsequently.

It will now be seen that when the exhaust port for the cylinder 4, defined by the annular groove 9 and the milled slot 12, is opened by the piston hammer 5, the air will flow radially through the slot 12, through the passages 11 into chamber 20, and through the holes 22 into chamber 21, then to ambient atmosphere. It will be noted that the passages 11 are slightly inclined so that the radial flow of air through the milled slot .12 will impinge on the Walls -of the passages 11 and be directed into the chamber 20 rather than into the chamber 19. This inclination of the passages 11 also assists in preventing the build-up of ice which may be formed as a result of the moisture contained in the exhaust air which is expanded as it passes from the cylinder chamber 4.

The forward chamber 19 is completely sealed except for communication with the forward ends of the passages Therefore, the main flow of air from the cylinder chamber does not pass into the chamber 1? but flows by the opening to the chamber. This chamber defines a resonating chamber of the side branch type which is activated by the air flowing past the chamber opening. The air flowing past the chamber opening contains sound pressure waves over a range of frequencies and these pressure waves are transmitted to the air within the resonating chamber. The chamber produces counterpressure waves at its resonant frequency and is efi'ective to cancel or damp out the activating waves of the exhaust air. It has been observed that this dampening effect is significant not only at the precise tuned frequency, but is also effective over a relatively broad range of frequencies on either side of the tuned frequency. It has been found that a resonating chamber of this type, tuned to a frequency in the area of 400 to 500 cycles per second produces a significant reduction in the noise produced by a rock drill in the lower end of the frequency spectrum.

The exhaust air flows through the chamber 20, entering the chamber from the passages 11 and leaving the chamber through the holes 22. The combined area of the holes 22 is substantially the same as the combined area of the passages 11 so that the air flowing into this chamber may expand but must be trecompressed before passing into the chamber 21. The chamber 20 defines an expansion chamber resonator which, being smaller than the chamber 19, is tuned to a higher frequency. This expansion chamber resonator functions in a manner similar to the side branch resonator chamber 19 in that it produces counterpressure waves at the tuned frequency which cancel the pressure waves at that frequency induced by the air flowing through the chamber; and this produces additional noise reduction in the area of the tuned frequency.

A silencer 27 is mounted within the housing chamber I 21, adjacent to the partition 18. This silencer consists of an assembly of thin rectangular plates 28, all of identical configuration, stacked in uniformly spaced relation to each other. The plates are assembled on a bracket 29 consisting of a plate having four transverse, parallel rods 30 projecting therefrom. Each of the silencer plates 28 is provided with suitable holes for receiving the rods 30, and the plates may be spaced from each other by means of suitable washers placed over the rods and between the adjacent plates. Each of the plates 23 and the bracket plate 29 is provided with three large holes 31, located respectively in the center and adjacent to the two ends of the plate; and two smaller holes 32 located between the holes 31. In order to support the silencer assembly within the housing 13, the partition 18 is provided with four holes to receive the ends of the bracket rods 30, and the bracket plate 29 is provided with flanges which are secured to the side walls 14, by means of bolts or rivets for example. The plates 28 are then confined in a stacked relation between the partition 18 and the bracket plate 29. In this assembled relation, the holes 31 in the silencer plates 28 and in the bracket plate 29 are aligned with each other and with respective holes 22 in the partition 18, as best seen in FIGS. 2, to define unobstructed flow paths through the silencer for the air entering the chamber 21 through the holes 22.

The silencer 27 does not fully occupy the space within the chamber 21; and the air flowing through the flow paths defined by the holes 31 is permitted to expand laterally between the plates to the exterior of the silencer asssembly. This expanding air also enters the chambers or flow paths defined by the holes 32 in the silencer plates 28 and in the bracket plate 29 so that some of the expanding air may flow forwardly through these flow paths. Due to the expansion of air laterally through the spaces between the silencer plates, the velocity of air in the main flow paths through the holes 31 is reduced as the air moves through the silencer assembly thereby reducing the jet noise induced in the air flowing from the chamber 20 and into the chamber 21 through the silencer 27.

A silencer, as above described, which has proved effective in reducing noise above 1,000 cycles per second, has been fabricated of nylon plates having a thickness of inch and spaced inch apart.

A generally wedged shaped, sound absorbing deflector 35 is mounted at the rearward end of the housing 13, partially closing the rearward end of the housing chamber 21, as best seen in FIGS. 1 and 5. This deflector is preferably constructed of a porous, sound-absorbing material, such as felt, and may be secured in the housing by cementing the deflector to the side walls and outer wall of the housing. As best seen in FIG. 1, the deflector presents a surface 36 which is inclined relative to the flow of air from the main flow paths through the silencer defined by the holes 31. The air, impinging on the surface 36, is deflected generally toward the adjacent wall of the back head 2 and flows out of the chamber 21 through the openings defined by the notches 24 in the side walls 14 to ambient atmosphere. While the exhaust air itself is deflected from the linear paths through the silencer 27, high frequency sound waves in this air stream do not deflect but pass into the sound absorbant body and are absorbed therein to eifectively reduce noise of the air passing from the chamber 21.

In FIGS. 6 through 11 there is shown another muffiing arrangement for a conventional type of rock drill. In FIG. 6 there is shown a casing portion 41 defining a cylinder chamber 42 at its forward end and a larger chamber 43 at its rearward end for a conventional valve block and distribution valve. A piston hammer 44 reciprocates within the cylinder chamber 43, and a forwardly extending reduced diameter stem 45 of the hammer is guided in a cylinder bushing and liner 46 mounted at the forward end of the casing 41. Longitudinal ribs 47 along the outside of the casing 41 enclose the usual air passages for controlling the rock drill.

The casing 41 is provided with an internal annular groove 49 intermediate the ends of the cylinder chamber 42. This groove is positioned to be exposed by both faces of the hammer, respectively, at the ends of forward and return strokes of the hammer. As best seen in FIGS. 6, 7 and 8, an external annular rib 50 extends partially around the casing 41, in the plane of the groove 49, and is provided with two arcuately shaped passages 51 which pass generally longitudinally through the rib 50. A milled slot 52 is cut into the rib 50 from the annular groove 49, in the plane of the groove, to communicate the annular groove with the passages 51. The exhaust air flowing from the chamber 42, then, passes radially through the slots 52 into the passages 51. The passages 51 are slightly inclined so that the air flowingfrom the slots 52 impinges on walls of these ports which are not perpendicular to, the direction of air flow from the slots 52.

A longitudinally extending box-like housing 54 is mounted on the outside of the casing 41 along one side thereof, enclosing the annular rib 50. The housing is defined by side walls 55, an outer wall 56, an end wall 57 at the rearward end thereof, and an end wall at the forward end defined by an extension of cylinder bushing 46. The side walls and the end wall 56 are secured to the casing by means of welding, for example; the side walls being secured to the longitudinal ribs 47, the inner edges of the side walls being indicated by the dotted line 58 in FIG. 6. A transverse partition 59 is joined to the rib 50, and divides the housing 54 into a rearward chamber 60 and a forward chamber 61. The side walls 55 are provided with notches 62 at the forward ends, as best shown in FIG. 6, to define exhaust openings from the forward chamber 61.

The rearward chamber 60 is sealed except for the communication with the rearward ends of the passages 51, as best seen in FIG. 8; and this chamber defines a side branch resonating chamber for the exhaust air which-flows from the cylinder chamber 42 through the milled slots 52 and the passages 51 into the forward chamber 61. The resonating chamber 60 is tuned to a relatively low frequency, in the range of 400 to 500 cycles per second, for example, to damp sound waves at frequencies which are produced by harmonics of the puffs of the exhaust air passing from the cylinder chamber 42.

A silencer 63, generally similar to the silencer 27 previously described, is mounted in the forward chamber 61 adjacent to the forward wall of the rib 50. The silencer 63 consists of an assembly of thin plates 64 generally in the shape of a half-moon, which are stacked in uniformly spaced relation to each other on a bracket 65. The bracket 65 includes a plate having a configuration similar to that of the plates 64 and three transversely extending rods. A

center rod 66 extends transversely through the bracket plate 65 and two outer rods 67 extend rearwardly from the ends of the bracket plate parallel to the center rod. The silencer plates 64 are each provided with a center hole and two end holes to accommodate the rods 66 and 67, and the plates are assembled on the rods in spaced relation, for example, by means of suitable washers interposed between the adjacent plates. As best shown in FIG. 10, the plates 64 are each provided with two arcuate openings 68 respectively between the holes for the bracket rods. The bracket 65 is provided with similar arcuate holes which are aligned with the holes 68 to provide linear flow paths through the silencer assembly. The silencer is mounted in the chamber 61 against the forward wall of the rib 50; and for this purpose, the rib 50 is provided with three holes positioned relative to the arcuate openings of the passages 51, as best seen in FIG. 9, to receive the rearward ends of the bracket rods 66 and 67 to align the holes 68 in the silencer plates with the passages 51.

As best seen in FIGS. 6' and 11, the bracket rod 66 extends forwardly from the bracket plate 65 and bears against the forward wall of the housing 54 defined by the cylinder bushing 46. This forwardly extending portion of the bracket rod 66 passes through and is supported by a deflector 71 which is secured in the forward end of the chamber 61 as by cementing, for example. As best seen in FIG. 11, the deflect-or 7-1 is V-shape'd in configuration and presents two surfaces 72 which are inclined relative to the direction of air flow from the silencer flow paths defined by the holes 68, and are disposed to the air laterally toward openings 62 in the side walls 55. The deflector 711 comprises a body of porous material, such as felt, for the purpose of deflecting the air toward the exhaust openings from the chamber 61, while absorbing high frequency sound waves in the air impinging against the deflector surfaces 72.

It will again be noted that the silencer 63 does not fully occupy the chamber 61, so that some of the air flow ing through the main flow paths defined by the plate holes 68 may expand laterally through the spaces between 6 the plates 64 and then pass from the chamber 61 to the ambient atmosphere through the exhaust openings 62.

In FIGS. 12 through 15, there is shown still another muffling arangement for a conventional type of rock drill. In FIG. 12, there is shown a casing portion 74 defining a cylinder chamber 75 at its forward end, for a reciprocating piston hammer 76, and a larger chamber 77 at its rearward end, for a valve block and distribution valve. The torwardly extending stem of the hammer is guided in a cylinder bushing and liner assembly 78. Again the casing includes longitudinal ribs for carrying necessary air passages.

An internal annular groove 79 is provided intermediate the ends of the cylinder chamber 75 and positioned to be exposed by the head of the piston hammer 76 after each of the power and return strokes. Five exhaust ports 80 are provided at one side of the casing 74, opening from the annular groove 79 to the exterior of the casing. These ports, in cooperation with the annular groove, de fine the exhaust openings from the cylinder chamber 75 which are opened at the end of each of the power and return strokes of the hammer.

An elongated box-like housing 82 is mounted on one side of the casing, enclosing the exhaust ports 80. This housing consists of parallel side walls 83 which are joined to the casing along a portion of its length as indicated by the dotted line 84 in FIG. 12, an outer wall 85 bridging the side walls, and an end wall 86 closing the housing at its rearward end. The housing 82 is coextensive in length with the casing portion 74; and the housing is provided with a transverse partition 87 intermediate its ends which divides the housing into a rearward chamber 88 and a forward chamber 89. The partition 77 is positioned forward of the exhaust ports 80 so that the exhaust ports open into the rearward chamber. The partition 87 is provided with three spaced holes 90 which communicate the two chambers 88 and 89. The side walls 83 are not joined to the casing along their entire length, but are provided with notches 91 at their forward ends, as indicated :by the dotted lines in FIG. 12, to define lateral openings from the chamber 89 at the forward end thereof. The forward end of the forward chamber 89 is partially closed as will be described subsequently.

The pulfs of exhaust air from the cylinder chamber 75 are exhausted through the exhaust ports 80 directly into the rearward chamber 88, and this air is then discharged from the chamber 88 through the holes 90 in the partition 87. The chaimlber '88 is dimensioned to define an expansion type resonating chamber tuned to absorb sound waves at .the lower end of the frequency spectrum which are created by the pufls of exhaust air discharging into the chamber. The total area of the holes 90 is substantially the same as the total area of the exhaust ports 80 so that the air entering the chamber 88 is expanded and then must be recompressed before discharging through the holes 90.

A silencer 92 is mounted within the forward chamber 89 adjacent to the forward wall of the partition 87; and this silencer has the same structure as the silencer 27 described with reference to FIGS. 1 through 5. This silencer consists of an assembly of thin rectangular plates 93, all of identical configuration, stacked in uniformly spaced relation to each other. The plates are assembled on a bracket 94 consisting of a plate having four transversely projecting parallel rods 95. Each of the silencer plates 93 is provided with suitable holes for receiving rods 95, and the plates may be spaced from each other by suitable washers placed over the rods and between the adjacent plates. Each of the plates 93 and the bracket plate 94 is provided with three large holes 96, located respectively in the center and adjacent to the two ends of the plate, and two smaller holes 97 located between the holes 96. In order to support the silencer assembly wlthint-he housing '82, the partition 87 is provided with and the bracket plate 94 is provided with flanges which are secured to the side walls 83, by means of bolts or rivets for example. The plates are then confined in stacked relation between the partition 87 and the bracket plate 94. In this assembled relation, the holes 96 in :the silencer plates 92 and in the bracket plate 93 are aligned with each other and with respective holes 90 in the partition 87 to define unobstructed flow paths through the silencer for the air entering the chamber 89 from the chamber 88 through the holes 90.

The silencer 92 does not fully occupy the. space within the chamber 89; and the air flowing through the flow paths defined by the holes 96 is permitted to expand radially between the silencer plates and to pass to the exterior of the silencer assembly. This expanding air also may enter the chambers or flow paths defined by the holes 97 in the silencer plates and the bracket plate, so that some of the expanding air may flow forwardly through these flow paths.

A generally wedge-shaped, sound absorbing deflector 88, .similar to the deflector 35 described heretofore, is mounted at the forward end of the housing 82, partially closing the forward end of the chamber 89, as best seen in FIGS. 12 and 15. The deflector 88 is preferably constructed of a porous, sound absorbing material, such as felt, and may be secured in the housing by cementing the deflector to the side walls and outer wall of the housing. As best seen in FIG. 12, the deflector 98 presents a surface 99 which is inclined relative to the flow of air issuing through the main flow paths through the silencer 92 defined by the holes 96 in the silencer plates. This air, impinging on the surface 99, is deflected generally toward the adjacent exterior Wall of the casing 74 and flows out of the chamber 89 through the openings, defined by the notches 91 in the side walls 83, to ambient atmosphere.

What have been described are combinations of mufliing devices with a reciprocating piston type air motor, for damping or otherwise reducing the noise induced in the exhaust air issuing from the motor.

What is claimed is:

1. In a pneumatic percussion tool the combination of a tool casing having a piston chamber and an exhaust port opening from said piston chamber; means on said casing defining first, second and third chambers, a first passage communicating said first and second chambers, a second passage communicating said second and third chambers, and an opening from said third chamber to ambient atmosphere; said exhaust port communicating with said first passage;

said first chamber being open only to said first passage, and thereby being open to the florw of exhaust air through said exhaust port and said first passage to define a side branch resonator for damping sound waves of a selected frequency range in the exhaust air;

said second chamber defining an expansion chamber resonator for damping sound waves of a selected frequency range in the exhaust air flowing into the chamber through said first passage and out of said chamber through said second passage;

a silencer for sound waves of a selected frequency range mounted in said third chamber adjacent to said second passage; said silencer comprising an assembly of thin plates stacked in uniformly spaced relation to each other; each of said plates having an opening, and the openings of said plates registering with each other and with said second passage to define a main flow path through said silencer for the exhaust air flowing from said second passage; the spaces between said plates defining auxiliary flow paths from said main flow path for the exhaust air flowing through said silencer;

a sound [absorbing deflector mounted in said third chamber adjacent to said silencer in registry with said silencer main flow path; said deflector presenting a surface inclined relative to said silencer main flow path and disposed to direct the flow of air from said main flow path to said opening from said third chamber; and said deflector comprising a porous body for absorbing sound waves in the air impinging against said inclined surface.

2. In a pneumatic tool the combination of a tool casing having a motor chamber and an exhaust port opening from said motor chamber; means on said casing defining a resonator chamber and a passage communicating said resonator chamber with ambient atmosphere; said resonator chamber cominunicating with said exhaust port and being dimensioned for damping low frequency sound waves in the exhaust air flowing from said motor chamber;

a silencer mounted in communication with said passage for damping high frequency sound waves in the air flowing through said passage; said silencer comprising means defining an unobstructed passageway providing a main flow path for the exhaust air flowing from said resonator chamber, the walls of said passageway having openings therethrough defining auxiliary flow paths from said main flow path for the exhaust air flowing through said silencer;

sound absorbing deflector means mounted in the main flow path of air flowing through said silencer to present a surface inclined to said main flow path; and said deflector means comprising a porous body for absorbing high frequency sound waves in the air impinging against said inclined surface.

3. In a pneumatic percussion tool the combination of a tool casing having a piston chamber and an exhaust port opening from said piston chamber; means on said casing defining resonator chamber, and a passage communicating said resonator chamber with ambient atmosphere; said resonator chamber communicating with said exhaust port and being dimensioned for damping low frequency sound waves in the exhaust air flowing from said piston chamber;

a silencer for high frequency sound waves mounted on said casing adjacent to said passage; said silencer comprising an assembly of thin plates stacked in spaced relation to each other; each of said plates having an opening, and the openings of said plates registering with each other and with said passage to define a main flow path through said silencer for the exhaust air flowing from said passage; the spaces between said plates defining auxiliary flow paths from said main flow path for the exhaust air flowing through said silencer;

a sound absorbing deflector mounted on said casing adjacent to said silencer, in registry with the silencer main flow path; said deflector presenting a surface inclined relative to said silencer main flow path to deflect the flow of air from said main flow path; and said deflector comprising a porous body for absorbing high frequency sound waves in the air impinging against said inclined surface.

4. In a pneumatic percussion tool the combination of a tool casing having a piston chamber and an exhaust port opening from said piston chamber; means on said casing defining first and second chambers, a passage communicating said chambers, and an opening from said second chamber to ambient atmosphere; said first chamber communicating with said exhaust port and being dimensioned to define a resonator chamber for damping low frequency sound waves in the exhaustair flowing from said piston chamber;

a silencer for high frequency sound waves mounted in said second chamber adjacent to said passage;

said silencer comprising an assembly of thin plates stacked in uniformly spaced relation to each other; each of said plates having an opening, and the openings of said plates registering with each other and with said passage to define a main flow path through said silencer for the exhaust air flowing from said passage; the spaces between said plates defining auxiliary flow paths from said main flow path for the exhaust air flowing through said silencer;

a sound absorbing deflector mounted in said second chamber adjacent to said silencer, in registry with said silencer main flow path; said deflector presenting a surface inclined relative to said silencer main flow path and disposed to direct the flow of air from said main flow path to said opening from said second chamber; and said deflector comprising a porous body for absorbing high frequency sound waves in the air impinging against said inclined surface.

5. The invention set forth in claim 3 wherein said exhaust port communicates with said passage; and wherein said resonator chamber is open only to said passage, and thereby to said exhaust port to define a side branch resonator for damping low frequency sound waves.

6. The invention set forth in claim 3 wherein said exhaust port opens only to said resonator chamber; wherein said passage is independent of said exhaust port; and wherein said resonator chamber defines an expansion chamber resonator for damping low frequency sound waves in the exhaust air flowing through said chamber.

7. In a pneumatic tool the combination of a tool casing having a motor chamber and an exhaust port opening from said motor chamber; means on said casing defining a resonator chamber, and a passage communicating said resonator chamber with ambient atmosphere; said resonator chamber communicating with said exhaust port and being dimensioned for damping low frequency sound waves in the exhaust air flowing from said motor chamber;

a silencer mounted in communication with said passage for damping high frequency sound waves in the air flowing through said passage; said silencer comprising a structure defining an elongated, unobstructed passageway providing a main flow path and outlet for the exhaust air flowing from said resonator chamber; and said structure defining numerous auxiliary passageways opening from said unobstructed passageway throughout its length to auxiliary outlets, providing auxiliary flow paths from said main flow path for the exhaust air flowing through said silencer.

8. In a pneumatic percussion tool the combination of a tool casing having a piston chamber and an exhaust port opening from said piston chamber; means on said casing defining a resonator chamber, and a passage communicating said resonator chamber with ambient atmosphere; said resonator chamber communicating with said exhaust port and being dimensioned for damping low frequency sound waves in the exhaust air flowing from said piston chamber;

a silencer for high frequency sound waves mounted on said casing adjacent to said passage; said silencer comprising an assembly of thin plates stacked in uniformly spaced relation to each other; each of said plates having an opening, and the openings of 'said plates registering with each other and with said passage to define a main flow path through said si lencer and a main outlet for the exhaust air flowing from said passage; and the spaces between said plates defining auxiliary flow paths-from said main flow path and auxiliary outlets for the exhaust air flowing through said silencer. 9. In a pneumatic percussion tool the combination of a tool casing having a piston chamber and an exhaust port opening from said piston chamber; means on said casing defining firs-t and second chambers, a passage communicating said chambers, and an open- -ing from said second chamber to ambient atmosphere; said first chamber communicating with said exhaust port and being dimensioned to define a reson-ator chamber for damping low frequency sound waves in the exhaust air flowing from said piston chamber;

a silencer for high frequency sound waves mounted in said second chamber adjacent to said passage; said silencer comprising an assembly of thin plates stacked in uniformly spaced relation to each other; each of said plates having an opening, and the openings of said plates registering with each other and with said passage; .said plate openings defining a main flow path through said silencer and a main outlet for the exhaust air flowing from said passage; and the spaces between said plates defining auxiliary flow paths from said main flow path and auxiliary outlets for the exhaust air flowing through said silencer.

10. The invention set forth in claim 8 wherein said exhaust port from said piston chamber communicates with said passage; and wherein said resonator chamber is open only to said passage, and thereby to said exhaust port to define a side branch resonator for damping low frequency sound waves.

11. The invention set forth in claim 8 wherein said exhaust port opening from said piston chamber opens only to said resonator chamber; wherein said passage defines an outlet passage for said resonator chamber independent from said exhaust port; and wherein said resonator chamber defines an expansion chamber resonator for damping low frequency sound waves in the exhaust air flowing through said chamber.

12. In a pneumatic tool the combination of a tool casing having a motor chamber and an exhaust port opening from said motor chamber; means on said casing defining a resonator chamber, and a passage communicating said chamber with ambient atmosphere; said resonator chamber communicating with said exhaust port and being dimensioned for damping low frequency sound waves in the exhaust air flowing from said motor chamber;

sound absorbing deflector means mounted on said cas ing in the path of the air flowing through said passage to present a surface inclined relative to said path; and said deflector comprising a porous body for absorbing high frequency sound waves in the air impinging against said inclined surface.

13. In a pneumatic percussion tool the combination of a tool casing having a piston chamber and an exhaust port opening from said piston chamber; means on said casing defining resonator chamber, and a passage communicating said chamber with ambient atmosphere; said resonator chamber communicating with said exhaust port and being dimensioned for damping low frequency sound waves in the exhaust air flowing from said piston chamber;

a sound absorbing deflector mounted on said casing in registry with said passage; said deflector presenting a surface inclined relative to said passage to deflect the flow of air from said passage; and said deflector comprising a porous body for absorbing high frequency sound waves in the air impinging against said inclined surface.

14. In a pneumatic percussion tool the combination of a tool casing having a piston chamber and an exhaust port opening from said piston chamber; means on said casing defining first and second chambers, a passage communicating said chambers, and an opening from said second chamber to ambient atmosphere; said first chamber communicating with said exhaust port and being dimensioned to define a resonator chamber for damping low frequency sound waves in the exhaust air flowing from said piston chamber;

sound absorbing deflector mounted in said second chamber in registry with the opening of said passage into said second chamber; said deflector presenting a surface inclined relative to said passage and disposed to direct the fiow of air from said passage to said opening from said second chamber; and said deflector comprising a porous body for absorbing high frequency sound waves in the air impinging against said inclined surface.

15. The invention setforth in claim 13 wherein said exhaust port communicates with said passage; and wherein said resonator chamber is open only to said passage, and thereby to said exhaust port to define a side branch resonator for damping low frequency sound waves.

16. The invention set forth in claim 13 wherein said exhaust port opening from said piston chamber opens only to said resonator chamber; wherein said passage is independent of said exhaust port; and wherein said resonator chamber defines an expansion chamber resonator for damping low frequency sound waves in the exhaust air flowing through said chamber.

17. In a pneumatic tool the combination of sound absorbing deflector means mounted in the main flow path of air flowing through said silencer to present a surface inclined relative to said main flow path; and said deflector means comprising a porous body for absorbing high frequency sound waves in the air impinging against said inclined surface.

18. In a pneumatic tool the combination of a tool casing having a motor chamber and an exhaust port opening from said motor chamber; means on said casing defining an exhaust chamber communicating with said exhaust port, and an opening from said chamber to ambient atmosphere;

silencer mounted in said exhaust chamber adjacent to said exhaust port for damping sound waves in the exhaust air flowing from said motor chamber; said silencer comprising an assembly of thin plates stacked in uniformly spaced relation to each other; each of said plates having an opening, and the openings of said plates registering with each other and said exhaust port to define a main flow path through said silencer for the exhaust air flowing from said exhaust port; the spaces between said plates defining auxiliary flow paths from said main flow path for the exhaust air flowing through said silencer;

sound absorbing deflector mounted in said exhaust chamber adjacent to said silencer, in registry with said silencer main flow path; said deflector presenting a surface inclined relative to said silencer main flow path and disposed to direct the flow of air from said main flow path to said opening from said exhaust chamber; and said deflector comprising a porous body for absorbing high frequency sound waves in the air impinging against said inclined surface.

19. In a pneumatic tool the combination of a tool casing having a motor chamber and an exhaust port opening from said motor chamber;

a silencer mounted on said casing in communication with said exhaust port for damping sound waves in the exhaust air flowing from said motor chamber; said silencer comprising a structure defining an elongated, unobstructed passageway providing a main flow path and outlet for the exhaust air flowing from said port; and said structure defining numerous auxiliary passageways opening from said unobstructed passageway throughout its length to auxiliary outlets, providing auxiliary flow paths from said main flow path for the exhaust air flowing through said silencer.

20. In a pneumatic tool the combination of a tool casing having a motor chamber and an exhaust port opening from said motor chamber; means on said casing defining an exhaust chamber communicating with said exhaust port, and an opening from said chamber to ambient atmosphere;

a silencer mounted in said exhaust chamber adjacent to said exhaust port for damping sound Waves in the exhaust air flowing from said motor chamber; said silencer comprising an assembly of thin plates stacked in uniformly spaced relation to each other; each of said plates having an opening, and the openings of said plates registering with each other and said exhaust port to define a main flow path through said silencer and a main outlet for the exhaust air flowing from said exhaust port; and the spaces between said plates defining auxiliary flow paths from said main flow path and auxiliary outlets for the exhaust air flowing through said silencer.

21. In a pneumatic tool the combination of a tool casing having a motor chamber and an exhaust port opening from said motor chamber;

a silencer mounted on said casing adjacent to said exhaust port for damping sound waves in the exhaust air flowing from said motor chamber; said silencer comprising an assembly of thin plates stacked in uniformly spaced relation to each other; each of said plates having an opening, and the openings of said plates registering with each other and with said exhaust port to define a main flow path through said silencer and a main outlet for the exhaust air flowing from said port; and the spaces between said plates defining auxiliary flow paths from said main flow path and auxiliary outlets for the exhaust air flowing through said silencer.

References Cited by the Examiner UNITED STATES PATENTS 2,073,480 3/1937 Jimerson 181-36 2,166,218 7/1939 Morrison 181--36 2,789,653 4/ 1957 Fannen 18136 2,966,138 12/ 1960 Quackenbush 181-36 FOREIGN PATENTS 356,864 9/1931 Great Britain.

471,431 9/ 1937 Great Britain.

842,192 7/1960 Great Britain.

LOUIS I. CAPOZI, Primary Examiner. LEO SMILOW, Examiner.

ROBERT S. WARD, Assistant Examiner. 

21. IN A PNEUMATIC TOOL THE COMBINATION OF A TOOL CASING HAVING A MOTOR CHAMBER AND AN EXHAUST PORT OPENING FROM SAID MOTOR CHAMBER; A SILENCER MOUNTED ON SAID CASING ADJACENT TO SAID EXHAUST PORT FOR DAMPING SOUND WAVES IN THE EXHAUST AIR FLOWING FROM SAID MOTOR CHAMBER; SAID SILENCER COMPRISING AN ASSEMBLY OF THIN PLATES STACKED IN UNIFORMLY SPACED RELATION TO EACH OTHER; EACH OF SAID PLATES HAVING AN OPENING, AND THE OPENINGS OF SAID PLATES REGISTERING WITH EACH OTHER AND WITH SAID EXHAUST PORT TO DEFINE A MAIN FLOW PATH THROUGH SAID SILENCER AND A MAIN OUTLET FOR THE EXHAUST AIR FLOWING FROM SAID PORT; AND THE SPACES BETWEEN SAID PLATE DEFINING AUXILIARY FLOW PATHS FROM SAID MAIN FLOW PATH AND AUXILIARY OUTLETS FOR THE EXHAUST AIR FLOWING THROUGH SAID SILENCER. 